The invention relates to bonding substrates through an ethylene-vinyl acetate hot melt adhesive composition.
Edgebanding is a process that involves bonding a strip of material, or edgeband, to a side edge of a wood substrate to cover the edge. Edgebands are applied to edges for various reasons including to cover exposed laminations, to create a more substantial panel appearance by attaching a thick edge, or to decorate the edge with a more finished or contrasting appearance. Examples of edgeband materials include wood, polyvinyl chloride, polypropylene, melamine, paper, laminate, and acrylonitrile butadiene styrene.
Specific types of edgebanding processes include xe2x80x9cstraight,xe2x80x9d xe2x80x9csoft formingxe2x80x9d and xe2x80x9ccontour banding.xe2x80x9d Soft forming includes applying an adhesive composition to a strip of material and then applying the strip to a base substrate that has formed, e.g., curved or rounded, edges. Contour banding involves applying the adhesive to the edgeband material and then applying the edgeband to the base substrate so that the edgeband follows the contours of the base substrate.
The hot melt adhesive compositions that are used to bond the edgeband to the base substrate are typically xe2x80x9cunfilledxe2x80x9d or xe2x80x9cfilled.xe2x80x9d Unfilled hot melt adhesive compositions are usually applied to a substrate with an applicator roller and tend to string. Stringing occurs when the composition fails to provide a neat break during a coating process resulting in the formation of long string-like strands of composition. The strings are carried away by the substrate being coated, and, upon finally breaking, snap back on the applicator roller, snap back on the board being coated, or are thrown from the coating apparatus. The stringing creates maintenance issues in that the strings must be removed from the board being coated and the pressure rollers. The buildup of strings on the pressure rollers can cause build up of adhesive on the boards.
Fillers have been added to hot melt adhesive compositions to reduce the stringing of the adhesive from the roller. Fillers have also been added to hot melt adhesives to decrease the cost of the adhesive and to improve the break action of the adhesive such that it provides a clean break from the roller during application. Fillers tend to dull saw blades and increase the viscosity of the adhesive over time at elevated temperatures.
During edgebanding, the hot melt adhesive is maintained in the molten state in the glue pot of the edgebanding apparatus for extended periods of time. The prolonged exposure to heat can cause the adhesive composition to darken in color, which can be aesthetically undesirable for an end product incorporating the adhesive. Hot melt adhesive compositions also tend to char after prolonged exposure to heat. The char sticks to the glue pot, rendering clean up difficult.
In one aspect, the invention features a hot melt adhesive composition that includes a) a first ethylene-vinyl acetate copolymer includes from about 25% vinyl acetate to about 30% vinyl acetate based upon the weight of the first copolymer and having a melt index of no greater than 4 g/10 min, b) a second ethylene-vinyl acetate copolymer includes no greater than about 28% vinyl acetate based upon the weight of the second copolymer and having a melt index of from about 400 g/10 min to about 2500 g/10 min, and c) hydrogenated petroleum hydrocarbon resin. In one embodiment, the second ethylene-vinyl acetate copolymer has a melt index from about 400 g/10 min to about 800 g/10 min. In another embodiment, the second ethylene-vinyl acetate copolymer has a melt index from 400 g/10 min to about 600 g/10 min. In some embodiments, the second ethylene-vinyl acetate copolymer comprises no greater than 20% vinyl acetate based upon the weight of the second copolymer. In other embodiments, the second ethylene-vinyl acetate copolymer comprises from about 14% to about 20% vinyl acetate based upon the weight of the second copolymer. In another embodiment, the second ethylene-vinyl acetate copolymer comprises from about 16% to about 20% vinyl acetate based upon the weight of the second copolymer.
In one embodiment, the hot melt adhesive composition includes from about 30% by weight to about 55% by weight the first ethylene-vinyl acetate copolymer. In other embodiments, the hot melt adhesive composition includes from about 15% by weight to about 30% by weight the second ethylene-vinyl acetate copolymer. In other embodiments, the hot melt adhesive composition of claim 1 includes from about 30% by weight to about 55% by weight the first ethylene-vinyl acetate copolymer, and from about 15% by weight to about 30% by weight the second ethylene-vinyl acetate copolymer.
In some embodiments, the hot melt adhesive composition includes from about 40% by weight to about 50% by weight the first ethylene-vinyl acetate copolymer, and from about 15% by weight to about 25% by weight the second ethylene-vinyl acetate copolymer. In other embodiments, the hot melt adhesive composition includes from about 25% by weight to about 40% by weight hydrogenated petroleum hydrocarbon resin. In another embodiment, the hot melt adhesive composition includes from about 30% by weight to about 40% by weight hydrogenated petroleum hydrocarbon resin.
In another embodiment, the hot melt adhesive composition further includes an agent selected from the group consisting of pigment, dye, and combinations thereof. In some embodiments, the pigment is selected from the group consisting of titanium dioxide, carbon black, compounded pigments, and combinations thereof.
In other embodiments, the composition, when molten, appears clear to the human eye. In one embodiment, the composition exhibits a Molten Gardner color of no greater than 4. In other embodiments, the composition exhibits a Molten Gardner color of no greater than 3. In another embodiment, the composition exhibits a Molten Gardner color of no greater than 2.
In one embodiment, the composition is essentially free of stringing when used in an edgebanding apparatus in which the composition is applied to a substrate using a roller at a substrate speed of at least 10 meters/minute. In another embodiment, the composition is essentially free of stringing when used in an edgebanding apparatus in which the composition is applied to a substrate using a roller at a substrate speed of at least 50 meters/minute.
In one embodiment, the composition exhibits a viscosity of no greater than 140,000 centipoise at 204xc2x0 C. In another embodiment, the composition exhibits a viscosity of from about 80,000 centipoise to about 140,000 centipoise at 204xc2x0 C. In other embodiments, the composition exhibits a viscosity of from about 100,000 centipoise to about 130,000 centipoise at 204xc2x0 C.
In some embodiments, the composition is essentially free of inorganic filler. In other embodiments, the composition further includes antioxidant.
In one embodiment, the composition exhibits no greater than 50% change in viscosity over a period of 200 hours at 204xc2x0 C. the composition exhibits no greater than 30% change in viscosity over a period of 200 hours at 204xc2x0 C.
In other embodiments, the hot melt adhesive composition includes a) a fist ethylene-vinyl acetate co polymer includes from about 25% vinyl acetate to about 30% vinyl acetate based upon the weight of the first co polymer and having a melt index of no greater than 4 g/10 min, b) a second ethylene-vinyl acetate copolymer includes from about 16% vinyl acetate to about 20% vinyl acetate based upon the weight of the second copolymer and having a melt index of from about 400 g/10 min to about 600 g/10 min, c) hydrogenated petroleum hydrocarbon resin, and d) antioxidant.
In another aspect, the invention features a method of bonding two substrates through a hot melt adhesive composition, the method includes contacting a first substrate with an adhesive composition described herein, and contacting the adhesive composition with a second substrate. In one embodiment, the method includes applying the composition to the first substrate at a coating weight from about 9 g/ft2 to about 20 g/ft2. In some embodiments, the method includes applying the composition to the first substrate at a coating weight from about 9 g/ft2 to about 17 g/ft2.
In other embodiments, the method further includes applying heat and pressure to the construction. In another embodiment, the contacting includes roller coating the adhesive composition onto the substrate. In some embodiments, the first substrate includes wood or a wood product. In other embodiments, the first substrate is a composite that includes cellulose fibers and binder composition.
In another embodiment, the first substrate is selected from the group consisting of particle board, fiber board, chip board, hard board, oriented strand board, and plywood.
In other embodiments, the first substrate comprises wood, and contacting the first substrate includes contacting an edge of the first substrate with the composition. In some embodiments, the second substrate is selected from the group consisting of wood, wood product, plastic, paper, and combinations thereof.
In some embodiments, the method includes edgebanding, soft forming, or contour banding.
In other aspects, the invention features an article that includes a first substrate, a second substrate bonded to the first substrate through a hot melt adhesive composition described herein. In one embodiment, the first substrate includes wood or a wood product. In other embodiments, the first substrate includes a composite includes cellulose fibers and binder composition. In some embodiments, the first substrate is selected from the group consisting of particle board, fiber board, chip board, hard board, oriented strand board, and plywood. In other embodiments, the first substrate includes wood, contacting the first substrate includes contacting an edge of the first substrate with the composition. In some embodiments, the second substrate is selected from the group consisting of wood, wood product, plastic, paper, and combinations thereof. In other embodiments, the article is selected from the group consisting of furniture, shelves, closet organizers, counter tops, and doors.
The hot melt adhesive composition is well suited to bonding an edgeband to wood and wood products. The composition can be applied at a relatively low coating weight while maintaining good adhesive bond strength, and exhibits good heat resistance and heat stability. The composition also breaks cleanly during a high speed edgeband coating operation resulting in low amounts of stringing.
Other features of the invention will be apparent from the following description of the preferred embodiments thereof, and from the claims.